Measurements were performed manually using ImageJ on at least
90 objects.
Morphological observations of the HDs and SDs were performed
by Atomic Force Microscopy (AFM) Nanoscope 5 (VEECO). Thin
polymer films of each PU were deposed on a glass plate and dried
for one night prior to imaging. Tapping mode phase images of
sample surfaces were made using NanoProbe tips PPP-NCL
(Nanosensor) for PU88 with a frequency of 153.2 kHz PU75 and
PU60 were analyzed with a NanoProbe tip SSS-NCH (Nanosensor)
at a frequency of 272 kHz.
Small Angle X-ray Scattering (SAXS) was used to investigate the
HD distribution. For that purpose, stacks composed of several layers
of films were analyzed in transmission mode in two different directions,
see Fig. 2. Patterns were acquired using a RU-300 generator
equipped with a copper anode (lCuKa ¼ 1.54 Å). The 1e2 mm
thick stack was placed at a distance of 60 cm from the 2D CCD
detector.
The field-induced thickness strain Sexp was measured on circulars
sample (25 mm of diameter) with a homemade setup based
on a double-beam laser interferometer measurement (Agilent
10889B) [15e17]. Samples were placed between two cylindrical
brass masses acting as conductive electrodes. A mirror was placed
on the upper electrode to reflect the laser beam. A bipolar electric
field was supplied by a high voltage amplifier (Trek10/10B) driven
with a function generator (Agilent 33250A). Measurements were
made at room temperature.